Device for treating a surface

ABSTRACT

A device for treating a surface, in particular to a cleaning robot, has a detection device for identifying the type of surface, which detection device has a light source for irradiating the surface with light and has a sensor for detecting the light which is reflected by the surface. In order to improve the identification of the type of surface, it is proposed that a three-dimensional screen panel which forms a plurality of partial volumes is associated with the sensor, wherein each partial volume is in each case associated with a different sensor subarea of the sensor, and wherein adjacent sensor subareas are optically separated from one another by means of the screen panel such that light is prevented from passing from a first partial volume to a second partial volume. Furthermore, the invention relates to a method for operating a device for treating a surface.

FIELD OF TECHNOLOGY

The invention relates to a device for treating a surface, in particularto a cleaning robot, having a detection device for identifying the typeof surface, which detection device has a light source for irradiatingthe surface with light and a sensor for detecting the light, which isreflected by the surface.

PRIOR ART

Devices of the above-mentioned type are well known in the prior art,thus in particular in the form of automatically movable cleaning robotsfor cleaning and/maintaining floors or floor coverings. For example, itcan be a vacuum cleaner and/or a wet mop.

Publication DE 10 2013 113 426 A1 (also published as US 2014/0166047 A1)relates for example to a cleaning device comprising a device forcreating photographs of a surface to be navigated, wherein a photo canbe evaluated with regard to the type of a floor covering, and wherein anidentified floor covering can be used with regard to a movement strategyof the cleaning device and/or with regard to a setting of cleaningparameters, such as distance to the floor, brush speed or the like.

Even though this cleaning device has proven itself in the prior art, acontinuous further development is nonetheless desired.

SUMMARY OF THE INVENTION

Based on the above-mentioned prior art, it is the object of theinvention to create a device comprising a detection device foridentifying the type of surface, in the case of which the type ofsurface can be identified with an even greater accuracy.

To solve the above-mentioned object, the invention proposes that athree-dimensional screen panel, which forms a plurality of partialvolumes, is associated with the sensor of the detection device, whereineach partial volume is in each case associated with a different sensorsubarea of the sensor, and wherein adjacent sensor subareas areoptically separated from one another by means of the screen panel suchthat light is prevented from passing from a first partial volume to asecond partial volume.

The screen panel thus serves as optical screen, which divides the sensorinto a plurality of, for example four, sensor subareas and whichoptically, i.e. photometrically, separates the individual sensorsubareas at the same time, so that the light reflected from the surfacehits only a sensor subarea of the sensor within only a partial volume ofthe screen panel. It is thus possible to embody the detection devicewith a measuring accuracy, which is increased as compared to the priorart, by means of only a single sensor, because the latter is divided bymeans of the screen panel into individual sensor subareas, which providefor a separate evaluation of the light, which hits the respective sensorsubarea. The detection device can thus be produced in a particularlysimple and cost-efficient manner. In addition, it is not required toread out the measuring data of a plurality of sensors—simultaneously orconsecutively—which impacts the duration of a measuring cycle. During ameasurement, the screen panel is preferably arranged near the floorabove the surface to be treated, so that the entry of ambient light intothe partial volumes of the screen panel is minimized and only the lightreflected on the surface by the light source of the detection devicecontributes to the measurement, which ultimately improves thereliability of the identification of the type of surface.

It is furthermore proposed that a separate light source is associatedwith each partial volume of the screen panel. By assigning a separatelight source for each partial volume of the screen panel, in particularfor each partial volume, the surface to be treated is illuminatedseparately with regard to each partial volume of the screen panel. Thescreen panel can furthermore be attached directly to the surface, sothat ambient light can no longer enter into the screen panel from theoutside. By associating a separate light source with each partialvolume, the corresponding subareas of the surface can be illuminated inthe same or in a different manner, so that an identical illuminatingsituation is or is not created within the different partial volumes.

In the alternative, it is proposed that a common light source isassociated with the screen panel, wherein a separate light exit elementof the light source, in particular an optical fiber, is associated witheach partial volume. According to this embodiment, it is not necessaryfor a separate light source to be installed for each partial volume. Infact, a common light source, the emitted light of which is guided intothe individual partial volumes by means of light-guiding elements, canbe associated with all partial volumes. Advantageously, the light sourceis thereby arranged outside of the partial volumes, so that this thusdoes not result in a loss of space. For example, the light source can bearranged outside of the screen panel, advantageously also on the devicehousing of the treatment device, wherein the light is coupled into eachindividual partial volume by means of a light-guiding element (opticalfiber). Advantageously, the light-guiding elements are optical fibers,because they are particularly cost-efficient and can be flexibly adaptedto the spatial situations of the screen panel or also of the devicehousing, respectively. Compared to the arrangement of a separate lightsource for each partial volume of the screen panel, a cost-efficientproduction of the detection device and thus also of the device fortreating the surface, can be attained by means of the common lightsource.

It is proposed that the light within the partial volume has a certainilluminating parameter for irradiating the surface, wherein theilluminating parameters within at least two partial volumes differ fromone another. As a result of this embodiment, the subareas of theilluminated surface can be illuminated in different ways, so thatdifferent features of the surface can be detected and the measuringresults of the different partial volumes or sensor subareas,respectively, can be combined to form a measuring result, which is morereliable as a whole. The surface to be measured is thus not onlyilluminated with light of a single illuminating parameter, but with aplurality of different illuminating parameters, for example with fourdifferent illuminating parameters in the case of four sensor subareas.As a result of this embodiment, a plurality of different surface typescan be differentiated with an ever higher accuracy. As a result of thedifferent illuminating parameters it is in particular also possible tonot only differentiate hard floors from carpeted floor, but in fact forexample also differentiate hard floors among one another, so that aquantity of moisture, which differs for each hard floor type, forexample, is applied to the surface, without damaging the surface by amoisture, which is too high. As a result of the use of differentilluminating parameters within the illuminating panel, features of thesurface, which do not become visible for example within a second partialvolume with a second illuminating parameter, emerge within a partialvolume with a first illuminating parameter. Depending on the type ofsurface, a certain type of illumination can thus make the emergence of afeature of the surface more difficult or easier. As a result of theillumination of the surface with a plurality of different illuminatingparameters, a plurality of simultaneous measuring results is thuscreated, which, in the special combination, allow drawing an even morereliable conclusion to the type of surface. As a result of theilluminating panel, the measurement with different illuminatingparameters is thus made possible, without the light portions of theindividual partial volumes influencing one another. Every light portionis thereby associated with a certain sensor subarea of a single, commonsensor, which significantly reduces the apparatus configuration of thedetection device. In the event of identical illuminating parameters, theadjacent subareas of the surface to be treated can for example beilluminated at the same angle to the light source and the sensor, sothat the measuring results of the partial volumes can be compared to oneanother and so that deviations of the subareas can possibly bedetermined in order to avoid the measuring of an artifact, which is nottypical for the surface to be treated.

It is proposed that the illuminating parameter is an angle-dependentradiant intensity of the light, an entry angle of the light onto theirradiated surface, an angle between the light source and the sensorand/or between the light exit area and the sensor, a distance of thelight source and/or of the light exit area to the irradiated surface, apolarization state of the light and/or an isotropy of the light. As aresult of these illuminating parameters, the surface is irradiated bymeans of the light source or by means of the light exit area of thelight source, respectively within each partial volume at a certain entryangle, a certain wavelength, polarization, isotropy or the like.Isotropy of the light is to be understood as a different direction ofthe beams of a beam bundle, wherein a parallelism of the beams of a beambundle is at hand in the case of a low isotropy. In the case ofcompletely isotropic light, the beams of a beam bundle, in contrast, arenot parallel to one another. The isotropy of the light can for examplebe attained by means of a reflection of the light emitted by the lightsource/the light exit area at a rough surface. To provide differentilluminating parameters, a punctiform light source can also be used forexample within a first partial volume, while a flat light source is usedin a second partial volume. The surface can furthermore be illuminateddirectly or indirectly. The surface can be illuminated perpendicularlyor at an angle unequal to 90°. It is furthermore also possible toilluminate the surface with a stripe pattern. This can be attained, forexample, in that a slit diaphragm is associated with the light source.Further illuminating parameters are conceivable.

It is furthermore proposed that an evaluation device, which is equippedto evaluate the light received by means of the sensor subarea, withregard to a certain surface parameter, in particular a gloss, a colorand/or a texture of the surface, is associated with the sensor.Advantageously, the evaluation device has a microprocessor and a storagefor storing measuring data as well as reference data of known surfaces.The evaluation device can either be arranged in the detection deviceitself or at a different subarea of the device for treating the surface.The evaluation device evaluates the received light with regard tocertain surface parameters, so that different features of the surface tobe identified are evaluated. These features can emerge for example onlyin the case of hard floors and/or can only be relevant for carpetedfloors. To determine the surface parameters, a certain illuminatingparameter may possibly be necessary within the associated partialvolume. To determine the color of the surface, for example, anillumination with white light is advisable. To identify a microscopicstructure of the surface, the use of light of a certain wavelength canfurthermore also be necessary.

The surface parameter can for example be a gloss, a color and/or atexture of the surface. For example, the measuring signal received bythe sensor subarea can thus be evaluated within a first partial volumeof the screen panel with regard to a gloss point, a wavelength-dependentreflection maximum, reflection spectrum or the like, so that aconclusion can be drawn to the type of surface. The existence of a glosspoint, for example, refers to a hard floor, because carpeted floorstypically do not show a gloss point. In the alternative or in addition,the color can also allow drawing a conclusion to a certain surface type.The texture of the surface is furthermore also of interest, because forexample carpets or carpeted floors, respectively, show a differentsurface structure than for example hard floors.

It is proposed that the evaluated surface parameters of at least twosensor subareas are different from one another. A different surfaceparameter is thus determined in each of the partial volumes of thescreen panel, so that the totality of the evaluated surface parameterswithin the entire screen panel leads to an overall reliableidentification of the type of surface. The more partial volumes orsensor subareas, respectively, the detection device has thereby, themore accurately the type of surface can be identified.

It is proposed that the evaluation device is equipped to logically linkthe surface parameters of at least two sensor subareas to one anotherand to compare them to reference data of known surfaces in order todetermine the type of surface. By combining the surface parameters of aplurality of sensor subareas, a logical combination is created, which ischaracteristic for the certain type of a surface. By using theevaluation device, the measured combination is compared with referencedata, which include combinations of surface parameters stored in thedata storage. The currently measured surface can thus be identifiedreliably. The larger the number of the measured surface parameters, themore reliable the type of surface can be identified.

It is furthermore proposed that the sensor is a camera chip, inparticular a CCD sensor or a CMOS sensor. The sensor surface of thecamera chip is thereby evaluated as a function of the arrangement of theindividual partial volumes, wherein, for example in the case of fourpartial volumes, the sensor surface is also divided into four sensorsubareas, advantageously of the same size. Each sensor subarea isthereby evaluated and/or read out coherently by the evaluation device,so that the measured surface parameter can be assigned unambiguously toa certain partial volume of the screen panel.

In addition to the above-described device for treating a surface, amethod for operating a device, in particular an above-described device,is also proposed with the invention, in the case of which the surface isirradiated with light, and light reflected from the surface is evaluatedto identify the type of surface. The method according to the inventionincludes that light is determined in a plurality of optically separatedpartial volumes of a three-dimensional screen panel associated with asensor, is irradiated onto the surface, and is reflected from thesurface onto a sensor subarea of the sensor, which is associated withthe respective partial volume, wherein an illuminating parameter of thelight emitted within a first partial volume differs from an illuminatingparameter of the light emitted within a second partial volume, andwherein the light received by the sensor subareas is evaluated withregard to surface parameters of the surface, which differ from oneanother. The execution and the features of the method thereby followanalogously to the explanations provided above with regard to the devicefor treating the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below by means ofexemplary embodiments.

FIG. 1 shows a device according to the invention in a perspective view,

FIG. 2 shows the device in a side view,

FIG. 3 shows a side view of a detection device,

FIG. 4 shows a bottom view of the detection device,

FIG. 5 shows a first partial volume of the screen panel,

FIG. 6 shows a second partial volume of the screen panel,

FIG. 7 shows a third partial volume of the screen panel,

FIG. 8 shows a fourth partial volume of the screen panel,

FIG. 9 shows an image captured by the sensor,

FIG. 10 shows a table with reference data for evaluation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a device 1 according to the invention, which is embodiedhere as automatically movable robotic vacuum cleaner. The device 1 hastravel wheels as well as an electric motor for driving the travelwheels. The device 1 can furthermore be equipped with a navigationdevice (not illustrated), which provides for the automatic orientationof the device 1 within a room. Said navigation device typically includesa device for identifying obstacles and room situations.

FIG. 2 shows the device 1 in a side view, wherein a detection device 2,which is installed in the device 1, for identifying the type of surface21 is illustrated in a dashed manner. With a detection side, thedetection device 2 is directed towards the surface 21 to be measured,here for example a carpeted floor.

FIG. 3 shows the detection device 2 in a schematic side view. Thedetection device 2 has a sensor 7, here a camera, comprising a camerachip (CCD chip), as well as a three-dimensional screen panel 12, whichis embodied in a screen-like manner and which supports the sensor 7 onits upper side. The screen panel 12 has a plurality of partial volumes13, 14, 15, 16, of which only two partial volumes 13, 14 can beidentified in the illustrated side view. A certain sensor subarea 8, 9,10, 11 of the sensor 7 is associated with each of the partial volumes13, 14, 15, 16. A separate light source 17, 18, 19, 20 is furthermorearranged in each partial volume 13, 14, 15, 16 (see FIGS. 5 to 8). Thescreen panel 12 is embodied in such a way that the partial volumes 13,14, 15, 16 are optically separated from one another by walls of thescreen panel 12 in such a way that no light can propagate between thepartial volumes 13, 14, 15, 16, i.e. light emitted in a certain partialvolumes 13, 14, 15, 16 cannot pass into another partial volume 13, 14,15, 16. The partial volumes 3, 14, 15, 16 are to thus be understood asareas of the screen panel 12, which are photometrically separated and inwhich a separate light source 17, 18, 19, 20 in each case emits lighthere, irradiates onto a subarea of the surface 21 to be identified, andwherein a sensor subarea 8, 9, 10, 11, which is irradiated with thelight reflected from the surface 21 of the sensor 7, is associated witheach partial volume 13, 14, 15, 16.

FIG. 4 shows the detection device 2 from below, i.e. viewed from thedirection of the surface 21 into the screen panel 12. The individualpartial volumes 13, 14, 15, 16 of the screen panel 12 can be seen, whichare in each case associated with a sensor subarea 8, 9, 10, 11 of thesensor 7.

FIGS. 5 to 8 in each case show one of the partial volumes 13, 14, 15, 16in a vertical section. The light emitted by the respective light source17, 18, 19, 20 has an illuminating parameter, which is characteristicfor the respective partial volume 13, 14, 15, 16, for irradiating thesurface 21. Different illuminating conditions of the surface 21 can thusbe created within the partial volumes 13, 14, 15, 16, and can bedetected by means of only one sensor 7 (which is common to all partialvolumes 13, 14, 15, 16). Due to the different illuminating parameters,different surface parameters, which are characteristic for the currentlymeasured surface 21, emerge on the respective sensor subarea 8, 9, 10,11. The signals received as a whole by the sensor 7 can be joinedlogically with one another and can be connected to form a total dataset, which provides insight into the type of surface 21.

FIG. 5 shows a first partial volume 13 of the screen panel 12, in whicha first light source 17 and a first sensor subarea 8 are arranged. Thelight source 17 is arranged within the partial volume 13 in such a waythat said light source perpendicularly irradiates the surface 21 to beidentified. The light source 17 thereby irradiates only a limitedsubarea of the surface 21, which only has a small surface portionrelative to the exit surface of the partial volume 13 of the screenpanel 12. Depending on the type of surface 21, a certain portion of thelight can reach from the surface 21 to the sensor subarea 8. If thesurface 21 is a carpeted floor, for example, the light is scattered onthe surface 21, so that a diffuse light portion hits the sensor subarea8. If, in contrast, it is a hard floor, the perpendicularly irradiatedsurface 21 reflects the light back substantially perpendicularly, sothat only a relatively small light portion hits the sensor subarea 8.Based on the so-called “gloss point”, hard floors can thus bedifferentiated from carpeted floors.

FIG. 6 shows a second partial volume 14, in which a second light source18 as well as a second sensor subarea 9 are arranged. The light source18 is arranged within the partial volume 14 in such a way that thesurface 21 is not irradiated directly. In fact, the light source 18 isdirected to a corner area of the partial volume 14, so that theradiation emitted by the light source 18 is reflected from the innerwall of the screen panel 12 and illuminates the surface 21 in ascattered and indirect manner. In addition, the light emitted by thelight source 18 is widened at the corner area, so that the irradiation,which hits the surface 12, hits the surface 21 from different angleswithin a widened cone of light. The scattered irradiation of differentsurfaces 21, such as, for example, hard floors and carpeted floors, oralso different hard floors and/or carpeted floors among one another, inturn, causes different reflection signals, so that a conclusion can bedrawn to the type of surface 21 by means of the light received by thesensor subarea 9. Here, the arrangement within the partial volume 14serves to identify a wood-typical hue, i.e. to identify the surfaceparameter “color”, and to identify the texture of the surface 21. If thetexture has a preferential direction, for example, a conclusion can verylikely be drawn that the surface 21 is a carpeted floor or a vinylflooring. In fact, a wooden floor is possible as surface 21, which has agrain.

FIG. 7 shows a third partial volume 15 comprising a third light source19 and a third sensor subarea 10. The light source 19 is orientedsubstantially parallel to the surface 21 with the optical axis, whereinthe emitted light partially hits the surface 21 directly at an obliqueangle due to the conically widened light bundle, and a different portionis reflected on a wall of the screen panel 12, and possible hits thesurface 21 in a scattered manner. The sensor subarea 10 receives thelight reflected from the surface 21, which will be analyzed here, forexample with regard to the surface parameter “portion of black pixels”.If the light signal received by the sensor subarea 10 has a particularlylarge portion of black pixels, a conclusion can be drawn to a carpetedfloor. If the portion of black pixels is small, a wood or PVC ispossible as surface 21, in contrast.

FIG. 8 shows the fourth partial volume 16 of the screen panel 12, inwhich three light sources 20 as well as one sensor subarea 11 arearranged. The light sources 20 are arranged in parallel to one another,so that the emitted light portions run substantially parallel to oneanother, and the light hits the surface 21 in a strip-shaped manner.This creates a strip pattern on the surface 21, which is to beidentified, the light/dark transitions of which allow drawing aconclusion to the type of surface 21. If the surface 21 is a carpetedfloor, for example, the transitions have an irregular structure. Thesmoother the surface 21, however, the sharper the light/darktransitions, for example in the case of PVC or in particular wood.

FIG. 9 shows the light signals detected as a whole by the sensor 7 inthe form of a camera image. The latter is separated with regard to theindividual sensor subareas 8, 9, 10, 11. Due to the differentilluminating parameters within the partial volumes 13, 14, 15, 16, eachsensor subarea signal thereby reflects a different surface parameter.The corresponding signals of the sensor subareas 8, 9, 10, 11 areillustrated here. The image associated with the sensor subarea 8 servesto determine the gloss point, the image associated with the sensorsubarea 9 serves to determine the texture, the image associated with thesensor subarea 10 serves to determine the portion of the black pixels inthe image, and the image associated with the sensor subarea 11 serves toevaluate the light/dark transitions. It can be seen here, for example,that the surface 21 does not show a gloss point, does not have apreferential direction of the texture, has a large portion of blackpixels, and the light/dark transitions are not straight lines. Thesesurface parameters are logically connected to one another to form atotal data set and, in order to determine the type of surface 21, arecompared to reference data of known surfaces 21, which are stored withina data storage of an evaluation device. If the currently measured dataset corresponds to a stored data set, the type of surface 21 can bedetermined reliably. The reference data stored in the data storage canbe stored as table. In the above-specified case, a table appears in theway, which is illustrated in FIG. 10, for example.

Advantageously, the method for identifying the type of surface 21 iscarried out while the device 1 travels across the surface 21. The sensor7 thereby operates continuously. With regard to each partial volume 13,14, 15, 16, a certain surface parameter is extracted. The surfaceparameters are logically connected to one another and are used toidentify the surface 21.

On principle, methods of supervised learning are used for theevaluation. These methods include for example a training phase, in whicha plurality of different surfaces 21 is shown to the evaluation device.The respective surfaces 21 are known and are stored inside the datastorage with their corresponding surface parameters. It is also possiblethereby that not only known surface parameters can be identified, butalso different similar surface parameters, which the evaluation devicecan associate automatically. Different types of a surface 21, thesurface parameters of which are not identical, but similar, can thusalso be identified, so that the evaluation device can associate them toa certain type of surface 21.

The further treatment of the surface 21 by means of the device 1 canthen be controlled with the knowledge of the type of the currentlymeasured surface 21. If the identified surface 21 is a carpeted floor,the device 1 will avoid moistening the surface 21, for example, and willlimit a cleaning process to a vacuuming and/or brushing, for example.

REFERENCE LIST

-   1 device-   2 detection device-   3 light source-   4 light source-   5 light source-   6 light source-   7 sensor-   8 sensor subarea-   9 sensor subarea-   10 sensor subarea-   11 sensor subarea-   12 screen panel-   13 partial volume-   14 partial volume-   15 partial volume-   16 partial volume-   17 light source-   18 light source-   19 light source-   20 light source-   21 surface

1. A device (1) for treating a surface (21), having a detection device(2) for identifying the type of surface (21), which detection device (2)has a light source (3, 4, 5, 6) for irradiating the surface (21) withlight and a sensor (7) for detecting the light, which is reflected bythe surface (21), wherein a three-dimensional screen panel (12), whichforms a plurality of partial volumes (13, 14, 15, 16), is associatedwith the sensor (7), wherein each partial volume (13, 14, 15, 16) is ineach case associated with a different sensor subarea (8, 9, 10, 11) ofthe sensor (7), and wherein adjacent sensor subareas (8, 9, 10, 11) areoptically separated from one another by means of the screen panel (12)such that light is prevented from passing from a first partial volume(13, 14, 15, 16) to a second partial volume (13, 14, 15, 16).
 2. Thedevice (1) according to claim 1, wherein a separate light source (17,18, 19, 20) is associated with each partial volume (13, 14, 15, 16) ofthe screen panel (12).
 3. The device (1) according to claim 1, wherein acommon light source (17, 18, 19, 20) is associated with the screenpanel, wherein a separate light exit element of the light source (17,18, 19, 20), in particular an optical fiber, is associated with eachpartial volume (13, 14, 15, 16).
 4. The device (1) according to claim 1,wherein the light within the partial volume (13, 14, 15, 16) has acertain illuminating parameter for irradiating the surface (21), whereinthe illuminating parameters within at least two partial volumes (13, 14,15, 16) differ from one another.
 5. The device (1) according to claim 4,wherein the illuminating parameter is an angle-dependent radiantintensity of the light, an entry angle of the light onto the irradiatedsurface (21), an angle between the light source (3, 4, 5, 6) and thesensor (7) and/or between the light exit area and the sensor (7), adistance of the light source (3, 4, 5, 6) and/or of the light exit areato the irradiated surface (21), a polarization state of the light and/oran isotropy of the light.
 6. The device (1) according to claim 1,wherein an evaluation device, which is equipped to evaluate the lightreceived by means of the sensor subarea (8, 9, 10, 11), with regard to acertain surface parameter, is associated with the sensor (7).
 7. Thedevice (1) according to claim 6, wherein the evaluated surfaceparameters of at least two sensor subareas (8, 9, 10, 11) are differentfrom one another.
 8. The device (1) according to claim 6, wherein theevaluation device is equipped to logically link the surface parametersof at least two sensor subareas (8, 9, 10, 11) to one another and tocompare them to reference data of known surfaces (21) in order todetermine the type of surface (21).
 9. The device (1) according to claim1, wherein the sensor (7) is a camera chip.
 10. A method for operating adevice (1) for treating a surface (21), wherein the surface (21) isirradiated with light, and light reflected from the surface (21) isevaluated to identify the type of surface (21), wherein light isdetermined in a plurality of optically separated partial volumes (13,14, 15, 16) of a three-dimensional screen panel (12) associated with asensor (7), is irradiated onto the surface (21), and is reflected fromthe surface (21) onto a sensor subarea (8, 9, 10, 11) of the sensor (7),which is associated with the respective partial volume (13, 14, 15, 16),wherein an illuminating parameter of the light emitted within a firstpartial volume (13, 14, 15, 16) differs from an illuminating parameterof the light emitted within a second partial volume (13, 14, 15, 16),and wherein the light received by the sensor subareas (8, 9, 10, 11) isevaluated with regard to surface parameters of the surface (21), whichdiffer from one another.